The invention is directed to improvements in magnet valves, particularly for anti-lock vehicle brake systems.
A known magnet valve of this kind, as an inlet valve, is part of a magnet valve assembly in an anti-lock brake system; the assembly comprises a total of three magnet valves actuated by one common electromagnet (U.S. Pat. No. 4,765,693). In this inlet magnet valve, the throttle is formed by a perforated disk that is located downstream of the valve inlet. At the same time, this perforated disk serves to support a restoring spring that urges the valve member in the valve closing direction. The valve member is coupled to the electromagnet in such a way that when there is no current through the electromagnet, the valve member is lifted from the associated valve seat counter to the restoring spring, and when there is current to the electromagnet the valve member is released by the restoring spring for the closing motion.
Parallel to the aforementioned magnet valve, a second magnet valve, also used as an inlet valve is disposed between the valve inlet and the valve outlet of the magnet valve assembly; this second magnet valve likewise has a perforated disk, but its diameter is substantially larger than the throttle diameter of the first perforated disk mentioned. The restoring spring is again supported on the perforated disk and on the valve member and urges the valve member in the closing direction of the second magnet valve. The magnet valve is coupled to the electromagnet via a spring acting counter to the restoring spring; the spring forces are adapted, taking into account the pressure forces acting on the valve member from the valve inlet and from the valve outlet, in such a way that once magnet excitation has been shut off, the valve member does not open until a pressure difference operative in the closing direction drops below a predetermined value.
As a result of the two parallel inlet magnet valves, actuated by the same electromagnet, it is achieved that when the anti-lock system is active, when there is a major pressure difference between the valve inlet and the valve outlet only the magnet valve containing the throttle is opened, so that the rise in brake pressure at the valve outlet and hence in the wheel brake cylinder is slowed down, while when the anti-lock system is not active, in other words upon brake pedal actuation, when there are only slight pressure differences between the valve inlet and the valve outlet, both magnet valves are opened, so that large flow cross sections are available and brake pressures in the wheel brake cylinder can be built up unhindered.
Yet a third magnet valve is actuated by the electromagnet; the third magnet valve is disposed as an outlet valve between the valve outlet and a relief line, and by means of the third magnet valve the pressure at the valve outlet and hence in the wheel brake cylinder can be reduced. The valve member of this outlet magnet valve is urged in the closing direction by a valve closing spring that closes the outlet valve when there is no current to the electromagnet. The valve member! is coupled to the electromagnet in such a way that when the electromagnet is triggered by a first current intensity, at which the two inlet valves are released by the restoring springs fox the closing motion, remains in its closing position, and does not lift from the associated valve seat counter to the force of the closing spring, or in other words open the outlet valve, until the electromagnet is triggered by a second, greater current intensity.
The two inlet valves and the outlet valve of the known magnet valve assembly together with the common electromagnet for driving the valve members form a 3/3-way magnet valve with which the brake pressure in the wheel brake cylinder can be built up and reduced again in throttled or unthrottled fashion. Structurally, this magnet valve assembly is very complicated, making its manufacture relatively expensive.